fix(ci): run test projects on CI; remove brittle OPL attribute tests (#2513)

## Problem

Three coupled issues, each hiding the next:

1. **CI passed despite failing tests, with no test logs.** ([example run](https://github.com/modernuo/ModernUO/actions/runs/28639143286/job/84931544255) — the `Test` step produced zero output and the job went green.)
2. **Two `EmitsLowerStatReqWhenPassed` tests** fail with `KeyNotFoundException: '1060435'`.
3. Once CI actually ran the tests, **~337 UOContent tests failed** with `FileNotFoundException: tiledata.mul was not found` — the test bootstrap force-loaded copyrighted client data that CI doesn't have.

## Root causes & fixes

### 1. CI ran zero tests (`fix(ci)`)
The `Test` step ran `dotnet test --no-restore`, but the `Build` step only restores/builds `Application` — never the test projects. Without a restore, the test projects have no `project.assets.json`, so `Microsoft.NET.Test.Sdk`'s targets aren't imported, they aren't recognized as test projects, and `dotnet test` runs the `VSTest` target against **zero** projects → no output, **exit 0**.

- Both jobs now run `dotnet test --logger trx --results-directory ./TestResults` (test projects restore and run) **plus a guard** that fails the job if no `.trx` is produced — a permanent backstop against silent zero-test passes.

### 2. Impossible OPL tests (`fix(ci)` + `test(opl)`)
#2501 deliberately emits `LowerStatReq` (`1060435`) **inline in each item**, not in `GetProperties`. A follow-up "fix" dropped the `lowerStatReq:` argument to make the tests compile but left the assertions expecting `1060435`.

- Removed the two impossible tests, then removed the **entire `Tests/PropertyList/` OPL attribute set** from #2501: these assert exact cliloc/value/order of OPL emission per item base — a one-time proof of the #2501 rewire, now a permanent tax on modding (any admin reorder/value change/added line reddens the build). The one non-trivial case (LowerStatReq) is what just broke, because the test was wrong. Inline emission stays covered by the `BaseArmor`/`BaseClothing` tests.

### 3. Tile-data-dependent tests crashed CI (`test(uocontent)`)
UOContent.Tests' collection-fixture constructor force-loaded `tiledata.mul` unconditionally. On CI (no client files) it threw, and xUnit failed **every test in the collection** with the same error — mostly collateral (packet/scheduler/spawner tests that don't need tile data).

- Mirror Server.Tests' graceful pattern: `TestServerInitializer` probes for `tiledata.mul` and only loads tile/multi data (and runs the tile-dependent configure steps) when present, exposing `TileDataLoaded` so the fixture no longer throws.
- Add a shared `TileDataRequirement.SkipIfMissing()` guard and apply it to exactly the **31** pathfinding/multi/AI tests that genuinely need real tile data (`[SkippableFact]`/`[SkippableTheory]`).

## Verification (all local)

| Scenario | Server.Tests | UOContent.Tests |
|---|---|---|
| **Client data absent (CI)** | 726 pass, 17 skip, **0 fail** | 469 pass, 32 skip, **0 fail** |
| **Client data present (dev)** | 726 pass, 0 skip, **0 fail** | 501 pass, 0 skip, **0 fail** |

- Full `dotnet test` exits **0**; TRX files produced; the no-test guard trips (exit 1) only when zero `.trx` are produced.

Projects/UOContent.Tests/Tests/Engines/Pathing/StepProbeTests.cs

@@ -124,9 +124,10 @@ public class StepProbeTests
         Assert.True(found, "Expected at least one fully-flat open cell in (1500..1532, 1600..1632)");
     }
 
-    [Fact]
+    [SkippableFact]
     public void ComputeMaskAt_BritainInnDense_HasCellWithBlockedDirections()
     {
+        TileDataRequirement.SkipIfMissing();
         // Invariant: inside the dense Britain inn region, at least one cell must have
         // at least one direction blocked by a static. Protects against a regression
         // where the baker reports everything as walkable (the original false-pass bug).
@@ -181,9 +182,10 @@ public class StepProbeTests
         }
     }
 
-    [Fact]
+    [SkippableFact]
     public void ComputeMaskAt_PinnedCell_TrammelOpenPlainOrigin()
     {
+        TileDataRequirement.SkipIfMissing();
         // PINNING test: locks specific output for Trammel (1500, 1600).
         // Cell at z=10 with mask 0xC1 (N + W + NW only walkable). The other five
         // directions are blocked by water (E/SE/S/SW are wet tiles, NE is shore).
@@ -214,9 +216,10 @@ public class StepProbeTests
         Assert.Equal((sbyte)10, result.GetWalkZ(Direction.Up));
     }
 
-    [Fact]
+    [SkippableFact]
     public void ComputeMaskAt_PinnedCell_BritainInnDenseOrigin()
     {
+        TileDataRequirement.SkipIfMissing();
         // PINNING test: locks specific output for Trammel (1480, 1610).
         // Cell at z=20 with mask 0x3F (N/NE/E/SE/S/SW walkable, W/NW blocked by
         // a wall to the west). All walkable directions stay flat at z=20.